Aims. We present the abundance measurements of several elements (Fe, Ca, Na, Ni, Ti, Al, Cr, Si) for 20 solar–type stars belonging to four Galactic open clusters: NGC 3680, IC 4651, Praesepe, and M 67. Oxygen abundances were in addition measured for most stars in each cluster apart from IC 4651. For NGC 3680, accurate abundance determinations using high–resolution spectra covering a large spectral domain are computed for the first time.Methods. We used UVES high–resolution, high signal–to–noise (S/N) ratio spectra and performed a differential analysis with respect to the sun, by measuring equivalent widths and assuming LTE.Results. The most surprising result is a measurement of significant supersolar metallicity for Praesepe ([Fe/H]=0.27±0.10). As for the other clusters, we confirm a supersolar metallicity for IC 4651 ([Fe/H]=0.12±0.05), a solar metallicity for M 67 ([Fe/H]=0.03±0.04) and a slight subsolar metallicity for NGC 3680 ([Fe/H]=-0.04±0.03). We find that the abundance ratios of almost all elements are solar, with the notable exception of oxygen in NGC 3680 and Praesepe, supersolar in the former cluster ([O/Fe]=0.2±0.05) and as low as [O/Fe]=-0.4±0.1 in the latter. Observations of several objects per cluster is required to obtain robust results, especially for those elements with a limited number of suitable lines.

Institute of Astrophysics and Space Sciences

Institute of Astrophysics and Space Sciences (IA) is a new but long anticipated research infrastructure with a national dimension. It embodies a bold but feasible vision for the development of Astronomy, Astrophysics and Space Sciences in Portugal, taking full advantage and fully realizing the potential created by the national membership of the European Space Agency (ESA) and the European Southern Observatory (ESO). IA resulted from the merging the two most prominent research units in the field in Portugal: the Centre for Astrophysics of the University of Porto (CAUP) and the Center for Astronomy and Astrophysics of the University of Lisbon (CAAUL). It currently hosts more than two-thirds of all active researchers working in Space Sciences in Portugal, and is responsible for an even greater fraction of the national productivity in international ISI journals in the area of Space Sciences. This is the scientific area with the highest relative impact factor (1.65 times above the international average) and the field with the highest average number of citations per article for Portugal.